Instance Metadata

What is instance data?

Instance data is the collection of all configuration data that cloud-init processes to configure the instance. This configuration typically comes from any number of sources:

  • cloud-provided metadata services (aka metadata)
  • custom config-drive attached to the instance
  • cloud-config seed files in the booted cloud image or distribution
  • vendordata provided from files or cloud metadata services
  • userdata provided at instance creation

Each cloud provider presents unique configuration metadata in different formats to the instance. Cloud-init provides a cache of any crawled metadata as well as a versioned set of standardized instance data keys which it makes available on all platforms.

Cloud-init produces a simple json object in /run/cloud-init/instance-data.json which represents standardized and versioned representation of the metadata it consumes during initial boot. The intent is to provide the following benefits to users or scripts on any system deployed with cloud-init:

  • simple static object to query to obtain a instance’s metadata
  • speed: avoid costly network transactions for metadata that is already cached on the filesytem
  • reduce need to recrawl metadata services for static metadata that is already cached
  • leverage cloud-init’s best practices for crawling cloud-metadata services
  • avoid rolling unique metadata crawlers on each cloud platform to get metadata configuration values

Cloud-init stores any instance data processed in the following files:

  • /run/cloud-init/instance-data.json: world-readable json containing standardized keys, sensitive keys redacted
  • /run/cloud-init/instance-data-sensitive.json: root-readable unredacted json blob
  • /var/lib/cloud/instance/user-data.txt: root-readable sensitive raw userdata
  • /var/lib/cloud/instance/vendor-data.txt: root-readable sensitive raw vendordata

Cloud-init redacts any security sensitive content from instance-data.json, stores /run/cloud-init/instance-data.json as a world-readable json file. Because user-data and vendor-data can contain passwords both of these files are readonly for root as well. The root user can also read /run/cloud-init/instance-data-sensitive.json which is all instance data from instance-data.json as well as unredacted sensitive content.

Format of instance-data.json

The instance-data.json and instance-data-sensitive.json files are well-formed JSON and record the set of keys and values for any metadata processed by cloud-init. Cloud-init standardizes the format for this content so that it can be generalized across different cloud platforms.

There are three basic top-level keys:

  • base64_encoded_keys: A list of forward-slash delimited key paths into the instance-data.json object whose value is base64encoded for json compatibility. Values at these paths should be decoded to get the original value.
  • sensitive_keys: A list of forward-slash delimited key paths into the instance-data.json object whose value is considered by the datasource as ‘security sensitive’. Only the keys listed here will be redacted from instance-data.json for non-root users.
  • merged_cfg: Merged cloud-init ‘system_config’ from /etc/cloud/cloud.cfg and /etc/cloud/cloud-cfg.d. Values under this key could contain sensitive information such as passwords, so it is included in the sensitive-keys list which is only readable by root.
  • ds: Datasource-specific metadata crawled for the specific cloud platform. It should closely represent the structure of the cloud metadata crawled. The structure of content and details provided are entirely cloud-dependent. Mileage will vary depending on what the cloud exposes. The content exposed under the ‘ds’ key is currently experimental and expected to change slightly in the upcoming cloud-init release.
  • sys_info: Information about the underlying os, python, architecture and kernel. This represents the data collected by cloudinit.util.system_info.
  • v1: Standardized cloud-init metadata keys, these keys are guaranteed to exist on all cloud platforms. They will also retain their current behavior and format and will be carried forward even if cloud-init introduces a new version of standardized keys with v2.

The standardized keys present:

v1._beta_keys

List of standardized keys still in ‘beta’. The format, intent or presence of these keys can change. Do not consider them production-ready.

Example output:

  • [subplatform]

v1.cloud_name

Where possible this will indicate the ‘name’ of the cloud the system is running on. This is different than the ‘platform’ item. For example, the cloud name of Amazon Web Services is ‘aws’, while the platform is ‘ec2’.

If determining a specific name is not possible or provided in meta-data, then this filed may contain the same content as ‘platform’.

Example output:

  • aws
  • openstack
  • azure
  • configdrive
  • nocloud
  • ovf

v1.distro, v1.distro_version, v1.distro_release

This shall be the distro name, version and release as determined by cloudinit.util.get_linux_distro.

Example output:

  • alpine, 3.12.0, ‘’
  • centos, 7.5, core
  • debian, 9, stretch
  • freebsd, 12.0-release-p10,
  • opensuse, 42.3, x86_64
  • opensuse-tumbleweed, 20180920, x86_64
  • redhat, 7.5, ‘maipo’
  • sles, 12.3, x86_64
  • ubuntu, 20.04, focal

v1.instance_id

Unique instance_id allocated by the cloud.

Examples output:

  • i-<hash>

v1.kernel_release

This shall be the running kernel uname -r

Example output:

  • 5.3.0-1010-aws

v1.local_hostname

The internal or local hostname of the system.

Examples output:

  • ip-10-41-41-70
  • <user-provided-hostname>

v1.machine

This shall be the running cpu machine architecture uname -m

Example output:

  • x86_64
  • i686
  • ppc64le
  • s390x

v1.platform

An attempt to identify the cloud platfrom instance that the system is running on.

Examples output:

  • ec2
  • openstack
  • lxd
  • gce
  • nocloud
  • ovf

v1.subplatform

Additional platform details describing the specific source or type of metadata used. The format of subplatform will be:

<subplatform_type> (<url_file_or_dev_path>)

Examples output:

  • metadata (http://168.254.169.254)
  • seed-dir (/path/to/seed-dir/)
  • config-disk (/dev/cd0)
  • configdrive (/dev/sr0)

v1.public_ssh_keys

A list of SSH keys provided to the instance by the datasource metadata.

Examples output:

  • [‘ssh-rsa AA…’, …]

v1.python_version

The version of python that is running cloud-init as determined by cloudinit.util.system_info

Example output:

  • 3.7.6

v1.region

The physical region/data center in which the instance is deployed.

Examples output:

  • us-east-2

v1.availability_zone

The physical availability zone in which the instance is deployed.

Examples output:

  • us-east-2b
  • nova
  • null

Example Output

Below is an example of /run/cloud-init/instance-data-sensitive.json on an EC2 instance:

{
 "_beta_keys": [
  "subplatform"
 ],
 "availability_zone": "us-east-1b",
 "base64_encoded_keys": [],
 "merged_cfg": {
  "_doc": "Merged cloud-init system config from /etc/cloud/cloud.cfg and /etc/cloud/cloud.cfg.d/",
  "_log": [
   "[loggers]\nkeys=root,cloudinit\n\n[handlers]\nkeys=consoleHandler,cloudLogHandler\n\n[formatters]\nkeys=simpleFormatter,arg0Formatter\n\n[logger_root]\nlevel=DEBUG\nhandlers=consoleHandler,cloudLogHandler\n\n[logger_cloudinit]\nlevel=DEBUG\nqualname=cloudinit\nhandlers=\npropagate=1\n\n[handler_consoleHandler]\nclass=StreamHandler\nlevel=WARNING\nformatter=arg0Formatter\nargs=(sys.stderr,)\n\n[formatter_arg0Formatter]\nformat=%(asctime)s - %(filename)s[%(levelname)s]: %(message)s\n\n[formatter_simpleFormatter]\nformat=[CLOUDINIT] %(filename)s[%(levelname)s]: %(message)s\n",
   "[handler_cloudLogHandler]\nclass=FileHandler\nlevel=DEBUG\nformatter=arg0Formatter\nargs=('/var/log/cloud-init.log',)\n",
   "[handler_cloudLogHandler]\nclass=handlers.SysLogHandler\nlevel=DEBUG\nformatter=simpleFormatter\nargs=(\"/dev/log\", handlers.SysLogHandler.LOG_USER)\n"
  ],
  "cloud_config_modules": [
   "emit_upstart",
   "snap",
   "ssh-import-id",
   "locale",
   "set-passwords",
   "grub-dpkg",
   "apt-pipelining",
   "apt-configure",
   "ubuntu-advantage",
   "ntp",
   "timezone",
   "disable-ec2-metadata",
   "runcmd",
   "byobu"
  ],
  "cloud_final_modules": [
   "package-update-upgrade-install",
   "fan",
   "landscape",
   "lxd",
   "ubuntu-drivers",
   "puppet",
   "chef",
   "mcollective",
   "salt-minion",
   "rightscale_userdata",
   "scripts-vendor",
   "scripts-per-once",
   "scripts-per-boot",
   "scripts-per-instance",
   "scripts-user",
   "ssh-authkey-fingerprints",
   "keys-to-console",
   "phone-home",
   "final-message",
   "power-state-change"
  ],
  "cloud_init_modules": [
   "migrator",
   "seed_random",
   "bootcmd",
   "write-files",
   "growpart",
   "resizefs",
   "disk_setup",
   "mounts",
   "set_hostname",
   "update_hostname",
   "update_etc_hosts",
   "ca-certs",
   "rsyslog",
   "users-groups",
   "ssh"
  ],
  "datasource_list": [
   "Ec2",
   "None"
  ],
  "def_log_file": "/var/log/cloud-init.log",
  "disable_root": true,
  "log_cfgs": [
   [
    "[loggers]\nkeys=root,cloudinit\n\n[handlers]\nkeys=consoleHandler,cloudLogHandler\n\n[formatters]\nkeys=simpleFormatter,arg0Formatter\n\n[logger_root]\nlevel=DEBUG\nhandlers=consoleHandler,cloudLogHandler\n\n[logger_cloudinit]\nlevel=DEBUG\nqualname=cloudinit\nhandlers=\npropagate=1\n\n[handler_consoleHandler]\nclass=StreamHandler\nlevel=WARNING\nformatter=arg0Formatter\nargs=(sys.stderr,)\n\n[formatter_arg0Formatter]\nformat=%(asctime)s - %(filename)s[%(levelname)s]: %(message)s\n\n[formatter_simpleFormatter]\nformat=[CLOUDINIT] %(filename)s[%(levelname)s]: %(message)s\n",
    "[handler_cloudLogHandler]\nclass=FileHandler\nlevel=DEBUG\nformatter=arg0Formatter\nargs=('/var/log/cloud-init.log',)\n"
   ]
  ],
  "output": {
   "all": "| tee -a /var/log/cloud-init-output.log"
  },
  "preserve_hostname": false,
  "syslog_fix_perms": [
   "syslog:adm",
   "root:adm",
   "root:wheel",
   "root:root"
  ],
  "users": [
   "default"
  ],
  "vendor_data": {
   "enabled": true,
   "prefix": []
  }
 },
 "cloud_name": "aws",
 "distro": "ubuntu",
 "distro_release": "focal",
 "distro_version": "20.04",
 "ds": {
  "_doc": "EXPERIMENTAL: The structure and format of content scoped under the 'ds' key may change in subsequent releases of cloud-init.",
  "_metadata_api_version": "2016-09-02",
  "dynamic": {
   "instance_identity": {
    "document": {
     "accountId": "329910648901",
     "architecture": "x86_64",
     "availabilityZone": "us-east-1b",
     "billingProducts": null,
     "devpayProductCodes": null,
     "imageId": "ami-02e8aa396f8be3b6d",
     "instanceId": "i-0929128ff2f73a2f1",
     "instanceType": "t2.micro",
     "kernelId": null,
     "marketplaceProductCodes": null,
     "pendingTime": "2020-02-27T20:46:18Z",
     "privateIp": "172.31.81.43",
     "ramdiskId": null,
     "region": "us-east-1",
     "version": "2017-09-30"
    },
    "pkcs7": [
     "MIAGCSqGSIb3DQ...",
     "REDACTED",
     "AhQUgq0iPWqPTVnT96tZE6L1XjjLHQAAAAAAAA=="
    ],
    "rsa2048": [
     "MIAGCSqGSIb...",
     "REDACTED",
     "clYQvuE45xXm7Yreg3QtQbrP//owl1eZHj6s350AAAAAAAA="
    ],
    "signature": [
     "dA+QV+LLCWCRNddnrKleYmh2GvYo+t8urDkdgmDSsPi",
     "REDACTED",
     "kDT4ygyJLFkd3b4qjAs="
    ]
   }
  },
  "meta_data": {
   "ami_id": "ami-02e8aa396f8be3b6d",
   "ami_launch_index": "0",
   "ami_manifest_path": "(unknown)",
   "block_device_mapping": {
    "ami": "/dev/sda1",
    "root": "/dev/sda1"
   },
   "hostname": "ip-172-31-81-43.ec2.internal",
   "instance_action": "none",
   "instance_id": "i-0929128ff2f73a2f1",
   "instance_type": "t2.micro",
   "local_hostname": "ip-172-31-81-43.ec2.internal",
   "local_ipv4": "172.31.81.43",
   "mac": "12:7e:c9:93:29:af",
   "metrics": {
    "vhostmd": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
   },
   "network": {
    "interfaces": {
     "macs": {
      "12:7e:c9:93:29:af": {
       "device_number": "0",
       "interface_id": "eni-0c07a0474339b801d",
       "ipv4_associations": {
        "3.89.187.177": "172.31.81.43"
       },
       "local_hostname": "ip-172-31-81-43.ec2.internal",
       "local_ipv4s": "172.31.81.43",
       "mac": "12:7e:c9:93:29:af",
       "owner_id": "329910648901",
       "public_hostname": "ec2-3-89-187-177.compute-1.amazonaws.com",
       "public_ipv4s": "3.89.187.177",
       "security_group_ids": "sg-0100038b68aa79986",
       "security_groups": "launch-wizard-3",
       "subnet_id": "subnet-04e2d12a",
       "subnet_ipv4_cidr_block": "172.31.80.0/20",
       "vpc_id": "vpc-210b4b5b",
       "vpc_ipv4_cidr_block": "172.31.0.0/16",
       "vpc_ipv4_cidr_blocks": "172.31.0.0/16"
      }
     }
    }
   },
   "placement": {
    "availability_zone": "us-east-1b"
   },
   "profile": "default-hvm",
   "public_hostname": "ec2-3-89-187-177.compute-1.amazonaws.com",
   "public_ipv4": "3.89.187.177",
   "reservation_id": "r-0c481643d15766a02",
   "security_groups": "launch-wizard-3",
   "services": {
    "domain": "amazonaws.com",
    "partition": "aws"
   }
  }
 },
 "instance_id": "i-0929128ff2f73a2f1",
 "kernel_release": "5.3.0-1010-aws",
 "local_hostname": "ip-172-31-81-43",
 "machine": "x86_64",
 "platform": "ec2",
 "public_ssh_keys": [],
 "python_version": "3.7.6",
 "region": "us-east-1",
 "sensitive_keys": [],
 "subplatform": "metadata (http://169.254.169.254)",
 "sys_info": {
  "dist": [
   "ubuntu",
   "20.04",
   "focal"
  ],
  "platform": "Linux-5.3.0-1010-aws-x86_64-with-Ubuntu-20.04-focal",
  "python": "3.7.6",
  "release": "5.3.0-1010-aws",
  "system": "Linux",
  "uname": [
   "Linux",
   "ip-172-31-81-43",
   "5.3.0-1010-aws",
   "#11-Ubuntu SMP Thu Jan 16 07:59:32 UTC 2020",
   "x86_64",
   "x86_64"
  ],
  "variant": "ubuntu"
 },
 "system_platform": "Linux-5.3.0-1010-aws-x86_64-with-Ubuntu-20.04-focal",
 "userdata": "#cloud-config\nssh_import_id: [<my-launchpad-id>]\n...",
 "v1": {
  "_beta_keys": [
   "subplatform"
  ],
  "availability_zone": "us-east-1b",
  "cloud_name": "aws",
  "distro": "ubuntu",
  "distro_release": "focal",
  "distro_version": "20.04",
  "instance_id": "i-0929128ff2f73a2f1",
  "kernel": "5.3.0-1010-aws",
  "local_hostname": "ip-172-31-81-43",
  "machine": "x86_64",
  "platform": "ec2",
  "public_ssh_keys": [],
  "python": "3.7.6",
  "region": "us-east-1",
  "subplatform": "metadata (http://169.254.169.254)",
  "system_platform": "Linux-5.3.0-1010-aws-x86_64-with-Ubuntu-20.04-focal",
  "variant": "ubuntu"
 },
 "variant": "ubuntu",
 "vendordata": ""
}

Using instance-data

As of cloud-init v. 18.4, any instance-data can be used in:

  • User-data scripts
  • Cloud config data
  • Command line interface via cloud-init query or cloud-init devel render

This means that any variable present in /run/cloud-init/instance-data-sensitive.json can be used, unless a non-root user is using the command line interface. In the non-root user case, /run/cloud-init/instance-data.json will be used instead.

Many clouds allow users to provide user-data to an instance at the time the instance is launched. Cloud-init supports a number of User-Data Formats.

Both user-data scripts and #cloud-config data support jinja template rendering. When the first line of the provided user-data begins with, ## template: jinja cloud-init will use jinja to render that file. Any instance-data-sensitive.json variables are surfaced as dot-delimited jinja template variables because cloud-config modules are run as ‘root’ user.

Below are some examples of providing these types of user-data:

  • Cloud config calling home with the ec2 public hostname and availability-zone
## template: jinja
#cloud-config
runcmd:
    - echo 'EC2 public hostname allocated to instance: {{
      ds.meta_data.public_hostname }}' > /tmp/instance_metadata
    - echo 'EC2 availability zone: {{ v1.availability_zone }}' >>
      /tmp/instance_metadata
    - curl -X POST -d '{"hostname": "{{ds.meta_data.public_hostname }}",
      "availability-zone": "{{ v1.availability_zone }}"}'
      https://example.com
  • Custom user-data script performing different operations based on region
## template: jinja
#!/bin/bash
{% if v1.region == 'us-east-2' -%}
echo 'Installing custom proxies for {{ v1.region }}
sudo apt-get install my-xtra-fast-stack
{%- endif %}
...

One way to easily explore what Jinja variables are available on your machine is to use the cloud-init query --format (-f) commandline option which will render any Jinja syntax you use. Warnings or exceptions will be raised on invalid instance-data keys, paths or invalid syntax.

# List all instance-data keys and values as root user
% sudo cloud-init query --all
{...}

# Introspect nested keys on an object
% cloud-init query -f "{{ds.keys()}}"
dict_keys(['meta_data', '_doc'])

# Test your Jinja rendering syntax on the command-line directly

# Failure to reference valid top-level instance-data key
% cloud-init query -f "{{invalid.instance-data.key}}"
WARNING: Ignoring jinja template for query commandline: 'invalid' is undefined

# Failure to reference valid dot-delimited key path on a known top-level key
% cloud-init query -f "{{v1.not_here}}"
WARNING: Could not render jinja template variables in file 'query commandline': 'not_here'
CI_MISSING_JINJA_VAR/not_here

# Test expected value using valid instance-data key path
% cloud-init query -f "My AMI: {{ds.meta_data.ami_id}}"
My AMI: ami-0fecc35d3c8ba8d60

Note

Trying to reference jinja variables that don’t exist in instance-data will result in warnings in /var/log/cloud-init.log and the following string in your rendered user-data: CI_MISSING_JINJA_VAR/<your_varname>.

Cloud-init also surfaces a command line tool cloud-init query which can assist developers or scripts with obtaining instance metadata easily. See query for more information.

To cut down on keystrokes on the command line, cloud-init also provides top-level key aliases for any standardized v# keys present. The preceding v1 is not required of v1.var_name These aliases will represent the value of the highest versioned standard key. For example, cloud_name value will be v2.cloud_name if both v1 and v2 keys are present in instance-data.json. The query command also publishes userdata and vendordata keys to the root user which will contain the decoded user and vendor data provided to this instance. Non-root users referencing userdata or vendordata keys will see only redacted values.

# List all top-level instance-data keys available
% cloud-init query --list-keys

# Find your EC2 ami-id
% cloud-init query ds.metadata.ami_id

# Format your cloud_name and region using jinja template syntax
% cloud-init query --format 'cloud: {{ v1.cloud_name }} myregion: {{
% v1.region }}'

# Locally test that your template userdata provided to the vm was rendered as
# intended.
% cloud-init query --format "$(sudo cloud-init query userdata)"

# The --format command renders jinja templates, this can also be used
# to develop and test jinja template constructs
% cat > test-templating.yaml <<EOF
  {% for val in ds.meta_data.keys() %}
  - {{ val }}
  {% endfor %}
  EOF
% cloud-init query --format="$( cat test-templating.yaml )"
- instance_id
- dsmode
- local_hostname

Note

To save time designing a user-data template for a specific cloud’s instance-data.json, use the ‘render’ cloud-init command on an instance booted on your favorite cloud. See devel for more information.